The present invention relates to a method of fabricating a nitride semiconductor for use in a short-wavelength semiconductor laser diode and the like expected to be applied to the fields of optical information processing and the like, a semiconductor device and a semiconductor light emitting device using the nitride semiconductor and a method of fabricating the same.
Recently, a nitride semiconductor of a group III-V compound, that is, a group V element including nitride (N), is regarded as a promising material for a short-wavelength light emitting device due to its large energy gap. In particular, a gallium nitride-based compound semiconductor (AlxGayInzN, wherein 0xe2x89xa6x, y, zxe2x89xa61 and x+y+z=1) has been earnestly studied and developed, resulting in realizing a practical blue or green light emitting diode (LED) device. Furthermore, in accordance with capacity increase of an optical disk unit, a semiconductor laser diode lasing at approximately 400 nm is earnestly desired, and a semiconductor laser diode using a gallium nitride-based semiconductor is to be practically used.
Now, a gallium nitride-based semiconductor laser diode according to Conventional Example 1 will be described with reference to drawings.
FIG. 37 shows the sectional structure of the conventional gallium nitride-based semiconductor laser diode showing laser action. As is shown in FIG. 37, the conventional semiconductor laser diode includes a buffer layer 302 of gallium nitride (GaN), an n-type contact layer 303 of n-type-GaN, an n-type cladding layer 304 of n-type aluminum gallium nitride (AlGaN), an n-type light guiding layer 305 of n-type GaN, a multiple quantum well (MQW) active layer 306 including gallium indium nitride layers having different composition ratios of indium (Ga1xe2x88x92xInxN/Ga1xe2x88x92yInyN, wherein 0 less than y less than xc3x97 less than 1), a p-type light guiding layer 307 of p-type GaN, a p-type cladding layer 308 of p-type AlGaN and a p-type contact layer 309 of p-type GaN successively formed on a substrate 301 of sapphire by, for example, metal organic vapor phase epitaxial growth (MOVPE).
An upper portion of the p-type cladding layer 308 and the p-type contact layer 309 is formed into a ridge with a width of approximately 3 through 10 xcexcm. A lamination body including the MQW active layer 306 is etched so as to expose part of the n-type contact layer 303, and the upper face and the side faces of the etched lamination body are covered with an insulating film 310. In a portion of the insulating film 310 above the p-type contact layer 309, a stripe-shaped opening is formed, a p-side electrode 311 in ohmic contact with the p-type contact layer 309 through the opening is formed over a portion of the insulating film 310 above the ridge. Also, on a portion of the n-type contact layer 303 not covered with the insulating film 310, an n-side electrode 312 in ohmic contact with the n-type contact layer 303 is formed.
In the semiconductor laser diode having the aforementioned structure, when a predetermined voltage is applied to the p-side electrode 311 with the n-side electrode 312 grounded, optical gain is generated within the MQW active layer 306, so as to show laser action at a wavelength of approximately 400 nm.
The wavelength of laser action depends upon the composition ratios x and y or the thicknesses of the Ga1xe2x88x92xInxN and Ga1xe2x88x92yInyN layers included in the MQW active layer 306. At present, the laser diode having this structure has been developed to show continuous laser action at room temperature or more.
Furthermore, laser action in the fundamental mode of the lateral mode along a horizontal direction (parallel to the substrate surface) can be shown by adjusting the width or height of the ridge. Specifically, the laser action of the fundamental lateral mode can be shown by providing a difference in the light confinement coefficient between the fundamental lateral mode and a primary or higher mode.
The substrate 301 is formed from, apart from sapphire, silicon carbide (SiC), neodymium gallate (NdGaO3) or the like, and any of these materials cannot attain lattice match with gallium nitride and is difficult to attain coherent growth. As a result, any of these materials includes a large number of mixed dislocations, namely, mixed presence of edge dislocations, screw dislocations and other dislocations. For example, when the substrate is made from sapphire, the substrate includes dislocations at a density of approximately 1xc3x97109 cmxe2x88x922, which degrades the reliability of the semiconductor laser diode.
As a method for reducing the density of dislocations, epitaxial lateral overgrowth (ELOG) has been proposed. This is an effective method for reducing threading dislocations in a semiconductor crystal with large lattice mismatch.
FIG. 38 schematically shows the distribution of crystal dislocations in a semiconductor layer of gallium nitride formed by the ELOG.
The outline of the ELOG will be described with reference to FIG. 38. First, a seed layer 402 of GaN is grown on a substrate 401 of sapphire by the MOVPE or the like.
Next, a dielectric film of silicon oxide or the like is deposited by chemical vapor deposition (CVD) or the like, and the deposited dielectric film is formed into a mask film 403 having an opening pattern in the shape of stripes with a predetermined cycle by photolithography and etching.
Then, a semiconductor layer 404 of GaN is formed on the mask film 403 by selective growth with portions of the seed layer 402 exposed from the mask film 403 used as a seed crystal by the. MOVPE or halide vapor phase epitaxial growth.
At this point, although a dislocation high-density region 404a where the dislocation density is approximately 1xc3x97109 cm2 is formed in a portion of the semiconductor layer 404 above the opening of the mask film 403, a dislocation low-density region 404b where the dislocation density is approximately 1xc3x97107 cmxe2x88x922 can be formed in a portion of the semiconductor layer 404 laterally grown on the mask film 403.
FIG. 39 shows the sectional structure of a semiconductor laser diode whose active area, namely, a ridge working as a current injecting region, is formed above the dislocation low-density region 404b. In FIG. 39, like reference numerals are used to refer to like elements shown in FIGS. 37 and 38.
When the current injecting region is formed above the dislocation low-density region 404b of the MQW active layer 306 in this manner, the reliability of the laser diode can be improved.
As a result of various examinations, the present inventors have found that semiconductor laser diodes according to Conventional Examples 1 and 2 have the following problems:
First, the problems of the growth method of a nitride semiconductor by the ELOG according to Conventional Example 2 will be described.
FIGS. 40(a) through 40(d) schematically show a state where polycrystals 405 of gallium nitride are deposited on the mask film 403 during the growth of the semiconductor layer 404 so as to degrade the crystallinity of the semiconductor layer 404.
Specifically, the mask film 403 having the openings is first formed on the seed layer 402 as is shown in FIG. 40(a), and plural semiconductor layers 404 are respectively grown by using, as the seed crystal, the portions of the seed layer 402 exposed in the openings of the mask film 403 as is shown in FIG. 40(b). At this point, since the mask film 403 is formed from a dielectric, plural polycrystals 405 that cannot be crystallized on a dielectric may be deposited on the mask film 403.
Next, as is shown in FIGS. 40(c) and 40(d), when the plural semiconductor layers 404 are grown to be integrated and to have a flat face with the polycrystals 405 deposited, a region 404c with poor crystallinity is formed on each polycrystal 405.
The present inventors have found that a laser diode with good characteristics cannot be obtained when the current injecting region is formed above the region 404c with poor crystallinity.
Second, the present inventors have found a problem that, in the semiconductor laser diode according to Conventional Example 1 or 2, it is difficult to increase the light confinement coefficient of the active layer along a direction vertical to the substrate surface.
FIG. 41 shows the relationship, in the semiconductor laser diode of Conventional Example 1, between the distribution of a refractive index of the MQW active layer 306 along the direction vertical to the substrate surface and the distribution of light intensity on a cavity facet. It is understood that part of generated light confined within the MQW active layer 306 leaks to the substrate 301 so as to generate a standing wave in the n-type contact layer 303. When the generated light is thus largely leaked from the MQW active layer 306 to the substrate 301, the light confinement ratio in the MQW active layer 306 is lowered, resulting in increasing the threshold value for laser action.
Also, FIG. 42 shows a far-field pattern of the laser diode of Conventional Example 1. In this drawing, the abscissa indicates a shift of emitted light from the normal direction of the cavity facet toward the horizontal direction (along the substrate surface), and the ordinate indicates light intensity of the emitted light. When the generated light is largely leaked to the substrate 301 as in Conventional Example 1, it is also difficult to obtain a unimodal far-field pattern. This goes for the semiconductor laser diode of Conventional Example 2.
Thirdly, the semiconductor laser diode of Conventional Example 1 has a problem that, in dividing plural laser diodes formed on a wafer into individual laser chips by, for example, cleavage, the facet of the cavity cannot be flat because the substrate of sapphire and the nitride semiconductor layer have different crystal planes. Specifically, as is shown in FIG. 43, sapphire forming the substrate 301 is easily cleaved on the (1-100) surface orientation, namely, the so-called M plane, and hence, the substrate is generally cleaved on the M plane of sapphire.
However, the M plane of a nitride semiconductor, for example, gallium nitride is shifted from the M plane of sapphire by 30 degrees in the plane, and hence, the M plane of sapphire accords with the (11-20) surface orientation, namely, the so-called A plane, of gallium nitride. Accordingly, when the substrate 301 is cleaved, cleaved ends of the buffer layer 302 and the lamination body above are shifted from that of the substrate 301 by 30 degrees so as to appear as an irregular face with level differences of several hundreds nm.
When the cavity facet is such an irregular face, mirror loss of laser at the cavity facet is increased, so as to increase the operation current of the semiconductor laser diode, which can degrade the reliability of the semiconductor laser diode. Furthermore, since the irregularities are randomly formed on the cavity facet, it is difficult to form with good reproducibility a cavity facet having a predetermined reflectance, which lowers the yield. Even when the cavity is formed not by cleavage but by dry etching, the same problem arises. Herein, a minus sign xe2x80x9cxe2x88x92xe2x80x9d used in a surface orientation indicates inversion of an index following the minus sign.
On the other hand, in the semiconductor laser diode of Conventional Example 2, the stripe-shaped opening of the mask film 403 for the selective growth is formed parallel to the M-axis of the semiconductor layer 404. This is because a rate of the lateral growth along the A-axis is much higher than in other directions, and hence, the selective growth can be effectively proceeded in a short period of time. Therefore, the dislocation low-density region 404b is parallel to the M-axis, and therefore, the cavity facet of the laser diode formed above the dislocation low-density region naturally accords with the M plane. As a result, it is necessary to cleave the substrate 401 on the A plane. Although sapphire can be easily cleaved on the M plane as described above, it cannot be easily cleaved on the A plane, which largely lowers the yield of the semiconductor laser diode.
Fourthly, it is known that an angle (tilt) between the C-axis of the seed layer 402 and the C-axis of the semiconductor layer 404 selectively grown above the seed layer 402 is approximately 0.1 through 1 degree in the ELOG.
On the other hand, when the ELOG is conducted again by using the dislocation low-density region 404b obtained by the ELOG as the seed crystal and covering the dislocation high-density region 404a with another mask film for selective growth, a nitride semiconductor crystal can be obtained merely from the dislocation low-density region 404b. Accordingly, a cavity having a facet according to the A plane can be formed on the crystal formed from merely-the dislocation low-density region 404b, resulting in largely increasing the yield in the cleavage.
When the cavity is formed along the A-axis, however, a waveguide is formed in a zigzag manner along the C-axis because of the tilt of the C-axis between the seed layer 402 and the selectively grown layer above the seed layer 402 as described above. Such a zigzag waveguide causes waveguide loss, resulting in a problem of increase of the operation current of the laser diode. Moreover, in a vertical cavity surface emitting laser diode array where plural cavitys are arranged in a direction vertical to the substrate surface, there arises a problem that the directions of emitting laser beams from the respective cavitys in the array do not accord with one another.
Fifthly, in the semiconductor laser diode of Conventional Example 2, the width of the dislocation low-density region 404b is as small as approximately 5 xcexcm, and it is necessary to align a photomask for the ridge with a width of approximately 3 xcexcm so as not to miss the dislocation low-density region 404b. Accordingly, high accuracy is required for alignment in the photolithography, which lowers the throughput and the yield in the photolithography. As a result, there arises a problem that productivity cannot be improved.
The present invention was devised in consideration of the aforementioned various conventional problems. A first object of the invention is improving crystallinity in ELOG, a second object is increasing a light confinement coefficient of a cavity, a third object is forming a cavity facet with small mirror loss, a fourth object is forming a cavity with small waveguide loss, and a fifth object is easing alignment of a mask for forming a ridge. By achieving these objects, the invention exhibits an excellent effect, in particular, in application to a laser diode for use in an optical disk unit.
The first method of fabricating a nitride semiconductor of this invention achieves the fist object and comprises the steps of forming, on a substrate, a first nitride semiconductor layer of AluGavInwN, wherein 0xe2x89xa6u, v, w 1 and u+v+w=1; forming, in an upper portion of the first nitride semiconductor layer, plural convexes extending at intervals along a substrate surface direction; forming a mask film for covering bottoms of recesses formed between the convexes adjacent to each other; and forming, on the first nitride semiconductor layer, a second nitride semiconductor layer of AlxGayInzN, wherein 0xe2x89xa6x, y, zxe2x89xa61 and x+y+z=1, by using, as a seed crystal, C planes corresponding to top faces of the convexes exposed from the mask film.
In the first method of fabricating a nitride semiconductor, the plural convexes are formed in the upper portion of the first nitride semiconductor layer and the bottoms of the recesses sandwiched between the convexes are covered with the mask film. Therefore, the second nitride semiconductor layer is grown by using, as the seed crystal, merely the C planes appearing on the top faces of the convexes of the first nitride semiconductor layer. As a result, even when polycrystals of the second nitride semiconductor layer are deposited on the mask film, the second nitride semiconductor layer grows over the polycrystals in the growth along a direction parallel to the substrate surface (lateral growth) owing to the mask film formed on the bottoms of the recesses between the convexes. Accordingly, the second nitride semiconductor layer is never prevented from growing by the polycrystals, resulting in attaining good crystallinity.
The second method of fabricating a nitride semiconductor of this invention achieves the first object and comprises the steps of forming, on a substrate, a first nitride semiconductor layer of AluGavInwN wherein 0xe2x89xa6u+v+w=1 and u+v+w=1; forming, in an upper portion of the first nitride semiconductor layer, plural convexes extending at intervals along a substrate surface direction; forming a mask for covering bottoms and at least part of walls of recesses formed between the convexes adjacent to each other; and forming, on the first nitride semiconductor layer, a second nitride semiconductor layer of AlxGayInzN, wherein 0xe2x89xa6x, y, zxe2x89xa61 and x+y+z=1, by using, as a seed crystal, portions of the convexes exposed from the mask film.
In the second method of fabricating a nitride semiconductor, even when polycrystals of the second nitride semiconductor layer are deposited on the mask film in growing the second nitride semiconductor layer in a direction parallel to the substrate surface, the second nitride semiconductor layer grows over the polycrystals owing to the mask film formed on the bottoms and at least part of the walls of the recesses between the convexes. Accordingly, the second nitride semiconductor layer is never prevented from growing by the polycrystals, resulting in attaining good crystallinity.
The first method of fabricating a nitride semiconductor device of this invention achieves the first object and comprises the steps of forming a first nitride semiconductor layer on a substrate; forming, in an upper portion of the first nitride semiconductor layer, plural grooves extending at intervals along a substrate surface direction; forming a mask film for covering bottoms of the grooves; growing, by using, as a seed crystal, C planes corresponding to portions of a top face of the first nitride semiconductor layer exposed from the mask film between the grooves, a lamination body including a second nitride semiconductor layer, an active layer formed from a third nitride semiconductor layer having a smaller energy gap than the second nitride semiconductor layer and a fourth nitride semiconductor layer having a larger energy gap than the active layer stacked in this order from a substrate side; and forming, on the lamination body, a current confinement part for selectively injecting carriers into the active layer.
In the first method of fabricating a nitride semiconductor device, the lamination body including the active layer is formed by the first method of fabricating anitride semiconductor of this invention. Accordingly, the active layer and the nitride semiconductor layers sandwiching the active layer in the vertical direction attain good crystallinity. As a result, the reliability of the semiconductor device can be largely improved.
The second method of fabricating a nitride semiconductor device of this invention achieves the first object and comprises the steps of forming a first nitride semiconductor layer on a substrate; forming, in an upper portion of the first nitride semiconductor layer, plural grooves extending at intervals along a substrate surface direction; forming a mask film for covering bottoms and at least part of walls of the grooves; growing, by using, as a seed crystal, portions of the first nitride semiconductor layer exposed from the mask film between the grooves, a lamination body including a second nitride semiconductor layer, an active layer formed from a third nitride semiconductor layer having a smaller energy gap than the second nitride semiconductor layer and a fourth nitride semiconductor layer having a larger energy gap than the active layer stacked in this order from a substrate side; and forming, on the lamination body, a current confinement part for selectively injecting carriers into the active layer.
In the second method of fabricating a nitride semiconductor device, the lamination body including the active layer is formed by the second method of fabricating a nitride semiconductor of this invention. Accordingly, the active layer and the nitride semiconductor layers sandwiching the active layer in the vertical direction attain good crystallinity. As a result, the reliability of the semiconductor device can be largely improved.
The third method of fabricating a nitride semiconductor of this invention achieves the first object and comprises the steps of forming, in an upper portion of a substrate, plural convexes extending at intervals along a substrate surface direction; and selectively growing a nitride semiconductor layer of AlxGayInzN, wherein 0xe2x89xa6x, y, zxe2x89xa61 and x+y+z=1, on top faces of the convexes of the substrate.
In the third method of fabricating a nitride semiconductor, not only the same effect as that of the first method of fabricating a nitride semiconductor can be attained but also there is no need to form a semiconductor layer as a seed crystal because the convexes in the shape of stripes are formed in the substrate itself. Furthermore, when the substrate is not a nitride semiconductor, there is no need to provide a mask film for selective growth, resulting in largely simplifying the fabrication process of the semiconductor.
The third method of fabricating a nitride semiconductor device of this invention achieves the first object and comprises the steps of forming, in an upper portion of a substrate, plural grooves extending at intervals along a substrate surface direction; selectively growing, on a top face of the substrate between the grooves, a lamination body including a first nitride semiconductor layer, an active layer formed from a second nitride semiconductor layer having a smaller energy gap than the first nitride semiconductor layer and a third nitride semiconductor layer having a larger energy gap than the active layer stacked in this order from a substrate side; and forming, on the lamination body, a current confinement part for selectively injecting carriers into the active layer.
In the third method of fabricating a nitride semiconductor device, the lamination body including the active layer is formed by the third method of fabricating a nitride semiconductor of this invention. Accordingly, the active layer and the nitride semiconductor layers sandwiching the active layer in the vertical direction attain good crystallinity and the fabrication process can be largely simplified, resulting in improving the productivity.
The first nitride semiconductor device of this invention achieves the second object and comprises a lamination body including a first nitride semiconductor layer, an active layer formed from a second nitride semiconductor layer having a larger refractive index than the first nitride semiconductor layer and a third nitride semiconductor layer having a smaller refractive index than the active layer successively stacked on a substrate; and a current confinement part formed on the lamination body for selectively injecting carriers into the active layer, and a gap is formed in a region below the current confinement part and between the active layer and the substrate.
In the first nitride semiconductor device, the gap with a smaller refractive index than the semiconductor is formed in the region below the current confinement part and between the active layer and the substrate. Accordingly, light generated in the active layer is less leaked to the substrate, resulting in increasing the confinement coefficient of the generated light in the active layer.
The second nitride semiconductor device of this invention achieves the second object and comprises a first nitride semiconductor layer formed on a substrate and including, in an upper portion thereof, plural convexes extending at intervals along a substrate surface direction; a second nitride semiconductor layer formed on the first nitride semiconductor layer with a lower face thereof in contact with top faces of the convexes; and a lamination body formed on the second nitride semiconductor layer and including a third nitride semiconductor layer, an active layer formed from a fourth nitride semiconductor layer having a larger refractive index than the third nitride semiconductor layer and a fifth nitride semiconductor layer having a smaller refractive index than the active layer, and the second nitride semiconductor layer has a refractive index smaller than or equivalent to a refractive index of the third nitride semiconductor layer.
In the second nitride semiconductor device, the second nitride semiconductor layer is grown by using, as the seed crystal, the top faces of the convexes formed in the shape of stripes in the upper portion of the first nitride semiconductor layer. Accordingly, gaps are formed between the convexes of the first nitride semiconductor layer below the second nitride semiconductor layer. Furthermore, the second nitride semiconductor layer has a refractive index smaller than or equivalent to that of the third nitride semiconductor layer, the light confinement coefficient in the active layer can be definitely increased by providing a current confinement part in the lamination body above the gap.
The fourth method of fabricating a nitride semiconductor device of this invention achieves the second object and comprises the steps of forming a first nitride semiconductor layer on a substrate; forming, in an upper portion of the first nitride semiconductor layer, plural grooves extending at intervals along a substrate surface direction; forming a mask film for covering bottoms of the grooves; growing, by using, as a seed crystal, C planes corresponding to portions of a top face of the first nitride semiconductor layer exposed from the mask film between the grooves, a lamination body including a second nitride semiconductor layer, a third nitride semiconductor layer, an active layer formed from a fourth nitride semiconductor layer having a larger refractive index than the third nitride semiconductor layer and a fifth nitride semiconductor layer having a smaller refractive index than the active layer stacked in this order from a substrate side; and forming, on the lamination body, a current confinement part for selectively injecting carriers into the active layer, and the step of growing the lamination body includes a sub-step of growing the second nitride semiconductor layer with a refractive index thereof smaller than or equivalent to a refractive index of the third nitride semiconductor layer.
According to the fourth method of fabricating a nitride semiconductor device, the second nitride semiconductor device of the invention can be definitely fabricated.
The fifth method of fabricating a nitride semiconductor device of this invention achieves the second object and comprises the steps of forming a first nitride semiconductor layer on a substrate; forming, in an upper portion of the first nitride semiconductor layer, plural grooves extending at intervals along a substrate surface direction; forming a mask film for covering bottoms and at least part of walls of the grooves; growing, by using, as a seed crystal, portions of the first nitride semiconductor layer exposed from the mask film between the grooves, a lamination body including a second nitride semiconductor layer, a third nitride semiconductor layer, an active layer formed from a fourth nitride semiconductor layer having a larger refractive index than the third nitride semiconductor layer and a fifth nitride semiconductor layer having a smaller refractive index than the active layer stacked in this order from a substrate side; and forming, on the lamination body, a current confinement part for selectively injecting carriers into the active layer, and the step of growing the lamination body includes a sub-step of growing the second nitride semiconductor layer with a refractive index thereof smaller than or equivalent to a refractive index of the third nitride semiconductor layer.
According to the fifth method of fabricating a nitride semiconductor device, the second nitride semiconductor device of the invention can be definitely fabricated.
The fourth method of fabricating a nitride semiconductor of this invention achieves the third object and comprises the steps of forming, on a substrate, a first nitride semiconductor layer of AluGavInwN wherein 0xe2x89xa6u, v, wxe2x89xa61 and u+v+w=1; forming, in an upper portion of the first nitride semiconductor layer, plural convexes extending at intervals along a substrate surface direction; forming a mask film for covering bottoms of recesses formed between the convexes adjacent to each other; and growing, on the first nitride semiconductor layer, plural second nitride semiconductor layers of AlxGayInzN, wherein 0xe2x89xa6x, y, zxe2x89xa61 and x+y+z=1, by using, as a seed crystal, C planes corresponding to top faces of the convexes exposed from the mask film, and the step of forming the plural second nitride semiconductor layers includes a sub-step of forming each of the second nitride semiconductor layers in a manner that a facet of the second nitride semiconductor layer parallel to a direction of extending the convexes is exposed every time the second nitride semiconductor layer extends over a given number of convexes among the plural convexes.
In the fourth method of fabricating a nitride semiconductor, each of the second nitride semiconductor layers is formed so as to expose the facet parallel to the direction of extending the convexes every time the second nitride semiconductor layer extends over a given number of convexes among the plural convexes formed in the upper portion of the first nitride semiconductor layer. Accordingly, when the facet is used as a cavity facet, the cavity facet is obtained without being affected by a cleaved end and an etched end, resulting in reducing mirror loss of the cavity facet.
The fifth method of fabricating a nitride semiconductor of this invention achieves the third object and comprises the steps of forming, on a substrate, a first nitride semiconductor layer of AluGavInwN, wherein 0xe2x89xa6u, v, wxe2x89xa61and u+v+w=1; forming, in an upper portion of the first nitride semiconductor layer, plural convexes extending at intervals along a substrate surface direction; forming a mask film for covering bottoms and at least part of walls of recesses formed between the convexes adjacent to each other; and forming, on the first nitride semiconductor layer, plural second nitride semiconductor layers of AlxGayInzN, wherein 0xe2x89xa6x, y, zxe2x89xa61 and x+y+z=1, by using, as a seed crystal, portions of the convexes exposed from the mask film, and the step of forming the plural second nitride semiconductor layers includes a sub-step of forming each of the second nitride semiconductor layers in a manner that a facet of the second nitride semiconductor layer parallel to a direction of extending the convexes is exposed every time the second nitride semiconductor layer extends over a given number of convexes among the plural convexes.
In the fifth method of fabricating a nitride semiconductor, each of the second nitride semiconductor layers is formed so as to expose the facet parallel to the direction of extending the convexes every time the second nitride semiconductor layer extends over a given number of convexes among the plural convexes formed in the upper portion of the first nitride semiconductor layer. Accordingly, when the facet is used as a cavity facet, the cavity facet is obtained without being affected by a cleaved end or an etched end, resulting in reducing mirror loss of the cavity facet.
The sixth method of fabricating a nitride semiconductor device of this invention achieves the third object and comprises the steps of forming a first nitride semiconductor layer on a substrate; forming, in an upper portion of the first nitride semiconductor layer, plural grooves extending at intervals along a substrate surface direction; forming a mask film for covering bottoms of the grooves; growing, by using, as a seed crystal, C planes corresponding to portions of a top face of the first nitride semiconductor layer exposed from the mask film between the grooves, plural lamination bodies each including a second nitride semiconductor layer, an active layer formed from a third nitride semiconductor layer having a smaller energy gap than the second nitride semiconductor layer and a fourth nitride semiconductor layer having a larger energy gap than the active layer stacked in this order from a substrate side; and forming, on each of the lamination bodies, a current confinement part for selectively injecting carriers into the active layer, and the step of growing the plural lamination bodies includes a sub-step of forming each of the lamination bodies in a manner than a cavity facet including the current confinement part is exposed every time the lamination body extends over a given number of C planes of the first nitride semiconductor layer.
In the sixth method of fabricating a nitride semiconductor device, the lamination bodies each including the active layer are formed by the fourth method of fabricating a nitride semiconductor of this invention. Accordingly, the cavity facet is obtained without being affected by a cleaved end or an etched end, resulting in reducing mirror loss of the cavity facet.
The seventh method of fabricating a nitride semiconductor device of this invention achieves the third object and comprises the steps of forming a first nitride semiconductor layer on a substrate; forming, in an upper portion of the first nitride semiconductor layer, plural grooves extending at intervals along a substrate surface direction; forming a mask film for covering bottoms and at least part of walls of the grooves; growing, by using, as a seed crystal, portions of the first nitride semiconductor layer exposed from the mask film between the grooves, plural lamination bodies each including a second nitride semiconductor layer, an active layer formed from a third nitride semiconductor layer having a smaller energy gap than the second nitride semiconductor layer and a fourth nitride semiconductor layer having a larger energy gap than the active layer stacked in this order from a substrate side; and forming, on each of the lamination bodies, a current confinement part for selectively injecting carriers into the active layer, and the step of growing the plural lamination bodies includes a sub-step of forming each of the lamination bodies in a manner than a cavity facet including the current confinement part is exposed every time the lamination body extends over a given number of portions of the first nitride semiconductor layer sandwiched between the grooves adjacent to each other.
In the seventh method of fabricating a nitride semiconductor device, the lamination bodies each including the active layer are formed by the fifth method of fabricating a nitride semiconductor of this invention. Accordingly, the cavity facet is obtained without being affected by a cleaved end or an etched end, resulting in reducing mirror loss of the cavity facet.
The third nitride semiconductor device of this invention achieves the third and fourth objects and comprises a first nitride semiconductor layer formed on a substrate and including, in an upper portion thereof, plural convexes extending at intervals along a substrate surface direction; a second nitride semiconductor layer formed on the first nitride semiconductor layer with gaps formed between side faces of the convexes; and a third nitride semiconductor layer formed on the second nitride semiconductor layer and including a cavity in the shape of a stripe into which confined carriers are injected, and the cavity is provided with a resonating direction of generated light substantially perpendicular to a direction of extending the convexes.
In the third nitride semiconductor device, the cavity is provided so that the resonating direction of generated light can be substantially perpendicular to the direction of extending the convexes. Therefore, when the direction of extending the convexes is, for example, the M-axis direction and the resonating direction of the cavity is the A-axis direction, the cavity facet accords with the A plane. Accordingly, when the substrate is formed from sapphire, the cleaved end of the substrate is the M plane, and hence, the cleave can be eased so as to improve the yield in the cleavage. Also, in this case, although the cavity crosses plural convexes working as the seed crystal, the waveguide loss is also reduced because the tilt in the C-axis between the first nitride semiconductor layer and the second nitride semiconductor layer is suppressed by the gaps formed in the first nitride semiconductor layer between the side faces of the convexes.
The eighth method of fabricating a nitride semiconductor device of this invention achieves the third and fourth objects and comprises the steps of forming a first nitride semiconductor layer on a substrate; forming, in an upper portion of the first nitride semiconductor layer, plural first grooves extending at intervals along one substrate surface direction; forming a first mask film for covering bottoms of the first grooves; growing a second nitride semiconductor layer by using, as a seed crystal, C planes corresponding to portions of a top face of the first nitride semiconductor layer exposed from the first mask film between the first grooves; forming, in an upper portion of the second nitride semiconductor layer, plural second grooves extending at intervals in the one substrate surface direction and having portions between the second grooves adjacent to each other in different positions, in a substrate surface direction, from the portions between the first grooves adjacent to each other; forming a second mask film for covering bottoms of the second grooves; growing a third nitride semiconductor layer including an active layer by using, as a seed crystal, C planes corresponding to portions of a top face of the second nitride semiconductor layer exposed from the second mask film between the second grooves; and forming, on the third nitride semiconductor layer, a current confinement part with a resonating direction of generated light substantially perpendicular to the one substrate surface direction.
According to the eighth method of fabricating a nitride semiconductor device, the third nitride semiconductor device of the invention can be definitely fabricated.
The ninth method of fabricating a nitride semiconductor device of this invention achieves the third and fourth objects and comprises the steps of forming a first nitride semiconductor layer on a substrate; forming, in an upper portion of the first nitride semiconductor layer, plural first grooves extending at intervals along one substrate surface direction; forming a first mask film for covering bottoms and at least part of walls of the first grooves; growing, a second nitride semiconductor layer by using, as a seed crystal, portions of the first nitride semiconductor layer exposed from the first mask film between the first grooves; forming, in an upper portion of the second nitride semiconductor layer, plural second grooves extending at intervals along the one substrate surface direction and having portions between the second grooves adjacent to each other in positions different, in a substrate surface direction, from portions between the first grooves adjacent to each other; forming a second mask film for covering bottoms and at least part of walls of the second grooves; growing a third nitride semiconductor layer including an active layer by using, as a seed crystal, portions of the second nitride semiconductor layer exposed from the second mask film between the second grooves; and forming, on the third nitride semiconductor layer, a current confinement part with a resonating direction of generated light substantially perpendicular to the one substrate surface direction.
According to the ninth method of fabricating a nitride semiconductor device, the third nitride semiconductor device of the invention can be definitely fabricated.
The semiconductor light emitting device of this invention achieves the fifth object and comprises a first semiconductor layer formed on a substrate and including, in an upper portion thereof, plural first convexes extending at intervals along a substrate surface direction; and a second semiconductor layer formed from a lamination body including an active layer on the first semiconductor layer in contact with the first convexes and including, in an upper portion thereof, plural second convexes extending in a direction the same as the first convexes at intervals different from the intervals of the first convexes, and carriers are injected into the active layer from a top face of one of the plural second convexes.
The second semiconductor layer generally formed by the ELOG includes a large number of threading dislocations in regions above the first convexes, and hence, it is necessary to form a current injecting region in a position excluding such regions. In the semiconductor light emitting device of this invention, since there is a difference between the formation cycle of the first convexes and the formation cycle of the second convexes, there appears, on the substrate, a region where the first convex accords with the second convex in a cycle larger than the formation cycles of these convexes. An alignment mark can be easily and definitely provided by using this large cycle, resulting in improving the yield and the throughput of the fabrication process.
The first method of fabricating a semiconductor light emitting device of this invention achieves the fifth object and comprises the steps of forming a first semiconductor layer on a substrate and forming, in an upper portion of the first semiconductor layer, plural first convexes extending at intervals along a substrate surface direction; forming, on the first semiconductor layer, a second semiconductor layer having a lower face in contact with the first convexes from a lamination body including an active layer, and forming, in an upper portion of the second semiconductor layer, plural second convexes extending in a direction the same as the first convexes at intervals different from the intervals of the first convexes; forming, on the substrate, a mark for aligning a mask for identifying a convex for injecting carriers into the active layer among the plural second convexes; and aligning the mask:by using the mark and forming one of the plural second convexes into a carrier injection part by using the mask.
According to the first method of fabricating a semiconductor light emitting device, the semiconductor light emitting device of this invention can be definitely fabricated.
The second method of fabricating a semiconductor light emitting device of this invention achieves the fifth object and comprises the steps of forming a first nitride semiconductor layer on a substrate; forming, in an upper portion of the first nitride semiconductor layer, plural grooves extending at intervals in a substrate surface direction; forming a mask film for covering bottoms of the grooves; growing, by using, as a seed crystal, C planes corresponding to portions of a top face of the first nitride semiconductor layer exposed from the mask film between the grooves, a lamination body including a second nitride semiconductor layer, an active layer formed from a third nitride semiconductor layer having a smaller energy gap than the second nitride semiconductor layer and a fourth nitride semiconductor layer having a larger energy gap than the active layer stacked in this order from a substrate side; forming, in an upper portion of the lamination body, plural convexes extending in a direction the same as the grooves at intervals different from the intervals of the grooves; and selecting one convex in a position above any of the grooves and in the vicinity of an area between the grooves among the plural convexes and forming the selected convex into a carrier injection part for injecting carriers into the active layer.
According to the second method of fabricating a semiconductor light emitting device, the semiconductor light emitting device of this invention can be definitely fabricated.
The third method of fabricating a semiconductor light emitting device of this invention achieves the fifth object and comprises the steps of forming a first nitride semiconductor layer on a substrate; forming, in an upper portion of the first nitride semiconductor layer, plural grooves extending at intervals in a substrate surface direction; forming a mask film for covering bottoms and at least part of walls of the grooves; growing, by using, as a seed crystal, portions of the first nitride semiconductor layer exposed from the mask film between the grooves, a lamination body including a second nitride semiconductor layer, an active layer formed from a third nitride semiconductor layer having a smaller energy gap than the second nitride semiconductor layer and a fourth nitride semiconductor layer having a larger energy gap than the active layer stacked in this order from a substrate side; forming, in an upper portion of the lamination body, plural convexes extending in a direction the same as the grooves at intervals different from the intervals of the grooves; and selecting one convex in a position above any of the grooves and in the vicinity of an area between the grooves among the plural convexes and forming the selected convex into a carrier injection part for injecting carriers into the active layer.
According to the third method of fabricating a semiconductor light emitting device, the semiconductor light emitting device of this invention can be definitely fabricated.